This invention pertains to a boost control device for internal combustion engines with an exhaust gas turbocharger comprising a bypass valve in a bypass line which is parallel to the exhaust gas turbine of the turbocharger, a motor operator for the bypass valve which can be loaded in the opening and closing directions and a control valve which feeds charge air to the motor operator as a function of temperature and, by means of another motor operator, as a function of boost pressure, in which the control valve feeds charge air to the motor operator of the bypass valve in the closing direction up to a pre-established boost pressure and wherein this feed can be vented into the environment by the control valve.
In a known device of this structure in accordance with DE-OS No. 26 50 033, actuation of the control valve as a function of the engine temerature is ensured by an additional electric motor operator which moves the housing of the control valve relative to its piston slide valve which, in turn, is itself actuated by a motor operator which is loaded with charging air. As the engine temperature rises, the control valve limits to low values the charging air pressure which acts in the direction of the closing of the bypass valve. With rising engine temperatures, this reduces the boost pressure for the engine and its performance as a protection against overload. The boost pressure and thus the engine's output are adjusted to a uniform value which is unaffected by ambient influences such as variations in temperature and air pressure.
An object of the invention is to provide a device of the aforementioned type such that the boost control takes into account changes in the ambient effects and adjusts the charging air pressure and thus the maximum engine output to a uniform value so that the climate and altitude of the site of operation have no effect on the maximum output of the engine.
This and other objects of the invention are attained by providing a boost control device of the aforementioned type with pressure control valve means which is loaded in the opening direction by the charge air, is loaded in the closing direction by means of a barometric plug, and which is exposed to the ambient pressure, and wherein means are provided for prestressing the barometric plug as a function of at least one of the ambient temperature and the charge air temperature.
According to a disclosed preferred embodiment of the invention the means for prestressing the barometric plug as a function of temperature includes an expanding element with a temperature-sensitive part that extends into a charge air line. Further, a wedge is provided in a plane extending transverse to the axis of the barometric plug, the wedge being displaced by the expanding element in opposition to the force of a compression spring.
The pressure control valve means controls a connecting line vented to the environment by a choke opening for the charge air to a motor operator of the control valve means and to the motor operator of the bypass valve in its opening direction. After the pressure control valve means opens, the control valve means blocks and vents to the environment exclusively the closing-direction feed of the charge air to the motor operator of the bypass valve.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one preferred embodiment in accordance with the present invention.